Organic matter decline and compaction are two major related soils degradation processes. Compaction changes the physical properties of soils with consequences on their biological functioning. Compost amendment is a current practice to compensate the loss of organic matter, which could contribute to increase soil aggregate stability and limit compaction. Furthermore, composts also modify the biological and chemical properties of soils. Therefore, both compost addition and compaction could affect the fate and impact of pesticides in soils, however this is poorly documented. Thus, the objective of this work was to study the effect of compost amendment and soil compaction on the fate and ecotoxicological impact of isoproturon (one of the most used cereals herbicides in Europe). Undisturbed soil cores (40 cm3) were sampled in the interfurrows of two plots located in a long-term French experimental site: one control plot (no compost) and one plot receiving a co-compost of sewage sludge and green waste. The last compost addition and isoproturon application were carried out 12 months and 20 months before sampling, respectively. Half of the soil samples were compacted leading to an increase in soil density of 0.3 g cm-3 as observed following wheeling. Then all samples were treated with 14C-isoproturon and incubated. Mineralization kinetics of isoproturon and overall balance of 14C were determined. The impact of isoproturon was studied through the measure of two enzyme activities, β-glucosidase and urease. Both compost amendment and compaction did not affect significantly the fate of isoproturon in soil. At the end of incubation, the mineralization of isoproturon reached a maximum of 20%. In all cases, the main dissipation pathway was the formation of non-extractable residues (70% of the initial 14C). Compaction had no effect on the fate of isoproturon probably because the reduction in porosity did not affect the habitable pore space accessible to degrading microbial communities [1]. The unexpected lack of effect of compost can be due to the chemical characteristics of this compost [2], to the lack of significant change in the soil properties after compost addition, or because the effect of compost on pesticide degrading activities strongly vary according with the time of sampling and the delay with the last amendments. The urease activity was not impacted by compost addition or compaction, maybe because the incubation conditions were not limiting for the biological activity or because of the repeated application of compost in the soil for ten years. However, the β-glucosidase was significantly affected by compaction except in the soil which was amended with compost. It seems that the compost acts as a buffer with regards to compaction. The study of the coupled effect of compost addition and compaction on the fate and impact of isoproturon showed that there were very few modifications compared to the not amended and not compacted soils. However further research should be performed with other composts, pesticides, and biological indicators.